Sensors are widely used in electronic devices to measure attributes of the environment and report a measured signal value. In many sensors and for many applications, an electrical current or voltage measurement is the directly sensed physical attribute that corresponds to the desired environmental characteristic.
Accurate current measurements are typically made by placing a series-connected resistor having a very well-characterized resistance in a sensor electrical circuit. The voltage across the resistor corresponds to the current using Ohm's Law, where the current equals the voltage divided by the resistance (or V=IR). An accurate current measurement thus requires an accurate voltage measurement as well as an accurate understanding of the resistance of the series-connected resistor. To reduce power losses in a sensor, the series-connected resistor typically has a small resistance and a large current can be needed to adequately measure the small resistance. It is important, therefore, to accurately measure a small voltage across a resistor in a current sensor.
One technique for accurate voltage measurements across a two-terminal device is four-point terminal sensing using four-point probes with two pairs of electrical connections, often called Kelvin connections, connected across a two-terminal device, such as a sense resistor. Four-terminal sensing uses two terminals (electrodes) for providing current and two separate terminals (electrodes) for sensing the voltage, thereby separating the current path through the resistor from the voltage drop across the resistor and eliminating the lead and contact resistance of the current circuit from the voltage measurement. The electrical connections used to sense the voltage are conventionally called sense contacts (or sense leads) and the electrical connections used to provide the current are conventionally called force contacts (or force leads). The four-wire connection improves the measurement accuracy by directly sensing the voltage drop across the resistor exclusive of the current supply connection. Since the voltage measurement device (voltmeter) typically has a very large impedance, any voltage drop across the voltmeter probes or contact is relatively small and can be ignored.
Three-point probes are also known that have only one electrical connection for voltage sensing separate from an electrical connection for providing current. The second electrical connection for voltage sensing is presumed to be the same as the one electrical connection.
Components are often tested in a test fixture to ensure that they are properly functional before being sold. It is important that the tests are accurate and representative of the component performance. To reduce testing costs, the component testing process can be done at a high rate, making the test process challenging. An electrical contact and testing platform is described in WO2011/141582. According to this testing design, three or more blades of a testing device are electrically contacted to each tested electrical contact (pin, lead) of a component. The three or more blades extend longitudinally in a direction parallel to the extension of the component electrical contact from the component package. The three or more blades facilitate an electrical connection between at least two of the blades and the component electrical contact so as to make an electrical connection between the blades and the contact even when the component is rotated or offset with respect to the blades. The three or more blades can correspond to and electrically contact each pair of the terminal connections of a four-point probe and provide more accurate current measurements of the component current use.
A semiconductor inspection apparatus for electrical testing of semiconductor devices is described in US 2008/238456. The inspection apparatus includes differently shaped sense and force probes that are stacked vertically on top of each other, whereby a sharp end portion of the sense probe directly contacts a larger flat portion of the force probe.
An electronic device testing apparatus including probe and probe card is described in US 2012/133383. The probes disclosed in this application comprise beam portions that are bent which makes them suitable for testing devices that have their input and output terminals arranged in a two-dimensional fashion, for example in two or more columns.
In order to benefit from the separate voltage-measurement Kelvin connection, it is important to locate the voltage-sensing terminals as close to the resistor as possible so as to reduce voltage-sensing lead resistance. Moreover, it is important to locate test leads in a position relative to a component (device) under test that is robust in the presence of variations in component position. There is a need, therefore, for devices, systems, structures, and methods that accurately position voltage sensing leads to a measured component in a test fixture.